Winches used in the hoisting of loads are getting increasingly large due to requirements for lifting heavier loads. In particular, winches used on drilling rigs for hoisting top drives and pipe strings tend to get larger in order to satisfy the increased load requirements. In certain applications it might be necessary to lift several thousand tons. Recently, there has been a desire to deploy winches that accommodate only a single or a few layers of wire rope on the winch drum, primarily to reduce wear on the wire rope from overlaying layers. In order to have available sufficient length of wire rope on the winch drum, the winch drum needs to be made larger, both in diameter and in the axial direction. Hence, a single layer winch, or a winch with only a very few layers of wire rope, tends to take up more space. It might also be desirable to run a plurality of wire ropes in parallel, for instance due to security reasons, which will make the axial space requirements even more pronounced. Space on drilling rigs, ships etc. where the winch typically is to be used is often restricted. Use of single layer winches drilling rig hoisting systems with several parallel wire ropes was described in patent application PCT/NO2014/050113, incorporated herein in its entirety by this reference. International winch standards require three to five wire rope safety turns as a backup and safety measure. These safety turns increase the required length of a winch drum even more, especially for single layer winches.
The present disclosure has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art by employing features that are specified in the description below and in the claims that follow.